If discovery's upper-airspace route can't be made no-error because of RAD
restrictions we don't yet model (PROF204 forbidden / PROF205 mandatory
routing common in Free Route Airspace), retry the whole discovery in the
conventional airway regime below the FRA floor (~FL195), where those
restrictions are far sparser. Adopt the low route only if it is fully
valid — the bar is no-error, and flying needlessly low isn't the answer
when neither passes, so the natural-FL route is kept otherwise.
Measured on the batch: no regression, and the fallback collapses the
FRA-blocked pairs from ~7-9 errors to 1-2 (near-miss). It delivers a
no-error plan for any pair that has a valid low-level alternative; the
remaining near-misses need the phase-2 mandatory-routing engine to close.
49 tests green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Alexandre
49dc74ef20